Choosing rotating shaft seal for submerged water application

[abeschneider]

Hi,
I'm trying to specify seals for an application as follows:
- submerged, freshwater (river water; not many particulates; some chance of suspended sand)
- max pressure: 3 psi
- max vacuum: 8 psi
- shaft speed: 520 RPM, continuous, single-direction (non reversing)
- surface speed: 1.4 m/s (4.5 ft/s)
- shaft hardness: 25-27 Rc
- desired life: at least 2 years continuous operation

I'm having trouble figuring out what seal to choose; it seems a mechanical seal is overkill given the low pressure and speed. Packing is leaky and maintenance-heavy. I've heard O-rings "are not good in dynamic situations". And lip seals damage the shaft and wear very quickly.

What is a good suggestion for the main shaft seal?

By the way, the shaft bearings (ball) are on the "dry" sides of the shaft (think of the application as a shaft going through a box filled with water under the above pressure). Should I specify both shaft seals at the "box walls" as well as bearing isolators?

Thanks for your help.

P.S. I posted this in the "Mechanical Seal Engineering" forum a few days ago, but haven't received any replies. Sorry if I offended anyone by re-posting in this forum.

 

[eromlignod]

How about a lip seal with a wear band under it?

Don
Kansas City

 

[Philrock]

You might also consider a pre-seal - a seal whose main purpose is to protect the main seal. I often use an o-ring as a pre-seal and a fluoropolymer u-cup as the main seal.

Since you have bi-directional pressure, you may need 2 seals at each sealing point.

By far your best resource for information on this will be seal manufacturers such as Parker or Bal Seal.

 

[Heckler]

I would contact

http://www.balseal.com/index.jsp

. Lip seals have to create a wear surface on the shaft. I did a miniature pump for a remote sensor application. Seal drag was very critical since this pump was solar powered. One thing we tried with great success is coating our shaft with NP3 (EN w/teflon codeposit)

http://www.coatingtechnologiesinc.com/services_plating.htmlThe

teflon codeposit really helped with reducing friction and bedding in of the seal.

Best Regards,

Heckler
Sr. Mechanical Engineer
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